The clean-up of legionella bacteria on the Bibby Stockholm barge could take around a week, an expert has said, after asylum seekers were evacuated from the vessel following the detection of the health hazard.
Legionella can cause legionnaires’ disease, a type of severe pneumonia, if small droplets of water containing the bacteria are inhaled. In some cases, legionnaires’ disease can be fatal.
David Harper, of Harper Water Management Group, said there were many different strains of legionella bacteria, with some more virulent than others.
According to public health agencies, the majority of human infections are down to L pneumophila serogroup 1.
“The first thing I’d ask [is] what serogroup it is” on the Bibby Stockholm, said Harper, saying the answer would affect the severity of control measures.
Harper, an expert in waterborne contamination prevention and emergency response, said that after evacuating the barge, the next step to controlling the hazard would be to disinfect the vessel.
“Anybody who goes on the barge, they must wear protective clothing, ie masks,” he said.
Harper said all the shower heads, tap nozzles and strainers within thermostatic mixing valves would have to be removed and disinfected. A 50 parts per million solution of sodium hypochlorite should then be added to the barge’s freshwater tanks, with each tap and toilet checked to ensure the water coming through them had the correct concentration of chlorine.
“You leave it in there for a minimum of one hour. Better is overnight or a couple of hours,” said Harper.
Sodium thiosulphate is then added to the system to reduce the chlorine levels, with each tap, toilet and outlet once again checked to ensure such levels are correct.
After that, said Harper, a flushing regime is required – a team who work their way around the barge each day, and opening every tap or water outlet for about five minutes and flushing every toilet.
The whole cleanup process, he said, takes about a week.
Even once passengers returned, the flushing regime should continue.
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“People in the room, they will be flushing the taps when they are having a shower, wash, go to the the toilet etc,” said Harper. But, he added: “You still have this team of people going around behind the scenes, flushing things that are not being used.”
Another approach to prevent a recurrence, said Harper, would be to inject the water system with chlorine dioxide or use a copper-silver ionisation system.
But with water systems that are unused, or only used infrequently, known to be a risk factor for legionella bacteria, it seems the outbreak on the Bibby Stockholm was far from a surprise.
“The main reason for legionella is that people don’t use the barge,” said Harper. “Stagnant water and legionella go together like no tomorrow.”
A spokesperson for the barge contractors Corporate Travel Management and the sub-contractors Landry & Kling said: “Landry & Kling are associates of Corporate Travel Management, who are working closely with local authorities to ensure housing solutions are safe and appropriate for service users.
“Landry & Kling, along with project partners, have followed all written recommendations made by Dorset Council Environmental Health.”
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